1. Field of the Invention
The invention relates to methods and systems for pulse charging automotive batteries.
2. Discussion
Battery cells in Hybrid Electric Vehicles (HEVs) may be electrically connected in series to provide high voltage. Over time, the state of charge (SOC) of individual cells may drift apart due to variations in intrinsic properties and environmental heat transfer. This may lead to reduced battery performance and life. As a result, it may be advantageous to rebalance the SOC of the cells.
Several methods may be used to rebalance the state of charge of battery cells. For example, some strategies individually adjust the state of charge of each cell through dedicated hardware. Such dedicated hardware, however, may not be practical in HEV applications due to cost and packaging constraints. Other strategies charge the cells until the lower SOC cells equalize, within some threshold, with respect to the higher SOC cells. Although these strategies may not require dedicated hardware, they may adversely affect cell life as the cells with higher SOC may become over-charged. Still other strategies begin charging the cells at a high current and gradually ramp to a small or “trickle” current as higher SOC cells approach 100%. These strategies may, however, be time consuming and subject to charge efficiency reductions at low currents where cell temperatures are approximately equal to ambient temperatures.